Swing rotor with holding pins fixed to branch arms and having connection part connecting the branch arms for centrifuge and centrifuge

ABSTRACT

Provided is a swing rotor for a centrifuge. The centrifuge includes a swing type rotor body having a plurality of holding pins and a plurality of buckets held by the holding pins in a swingable manner. On the rotor body, a connection part is formed to connect two branch arms that diverge from an arm part on an outer peripheral side. A thickness-reduced part penetrating in the same direction as a driving shaft is formed in a region surrounded by the two branch arms on an inner peripheral side of the connection part. Since the branch arms deform accordingly to a certain extent, partial concentration of the stress applied on the holding pins due to a centrifugal load can be alleviated. Thus, the lifespan of the centrifuge can be improved and the centrifugal separation operation can be stabilized.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Japan application serialno. 2014-220926, filed on Oct. 30, 2014. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a swing rotor type centrifuge (centrifugalseparator) used for separating a sample in the fields of medicine,pharmacy, genetic engineering, biotechnology, and so on, andparticularly relates to an improvement in the shape of a swing rotorthat holds swinging buckets.

Description of Related Art

A centrifugal separator is a device, which includes a rotor capable ofaccommodating a plurality of sample containers filled with samplestherein and a driving means, such as a motor, rotationally driving therotor and rotates the rotor in a rotor chamber to apply a centrifugalforce so as to centrifugally separate the samples. A swing rotor forcentrifuge is a device for rotating buckets, which accommodate samplecontainers having a bottomed part and filled with samples therein, in astate of holding the buckets swingable with respect to the swing rotorbody. A centrifugal load of the bucket is held by a set of holding pins(convex parts) disposed on opposite surfaces of arms of the swing rotorbody. Concave parts are formed on two side surfaces of the bucket toengage with the cylindrical surfaces on the outer peripheral side of theholding pins of the swing rotor body, and the concave parts are hungdownward from the top of the holding pins and are held by the holdingpins in a slidable manner. A gap that does not interfere with thesliding exists between the front end surfaces of the holding pins andthe opposite surfaces of the concave parts of the bucket (orthogonalplane). In terms of the positional relationship, the central axis of thebucket and the driving shaft of the motor are parallel to each other(swing angle θ=0°) when the rotor is stationary. However, as therotation speed of the rotor increases, the bucket swings due to thecentrifugal force. The bucket rotates around the swing axis so thatθ>0°, and then enters a substantially horizontal state (θ≈90°) when arotation speed that is sufficient for generating a centrifugal force tomake the bucket horizontal is reached. Thereafter, the centrifugalseparation operation ends, and the swing angle θ decreases as therotation speed drops and becomes 0° (θ=0°) when the rotation of therotor stops. Thus, the relative angle between the central axis of thebucket and the driving shaft of the swing rotor changes according to thecentrifugal force during the centrifugation.

The load of the bucket, the sample, and the sample container during thecentrifugation is held by the convex parts (holding pins) that aredisposed to face each other on the swing rotor body. When the swingrotor body rotates at a high speed, the holding pins are slightlydeformed by the centrifugal force they receive from the bucket, andparticularly stress is concentrated near the bases of the convex parts.For this reason, various measures have been considered in order toprevent the stress from concentrating on a particular portion of theholding pins. According to Japanese Patent Publication No. 2012-101203,for example, the holding pin 25 has a shape that is narrowed down toreduce the outer diameter on the aim side, and the diameter of thesliding surface in contact with the pin receiving part of the bucket isincreased, and a narrowed shape is formed on the front end side of thesliding surface, so as to prevent the stress received by the holdingpins from concentrating on a particular portion while maintaining thecontact area of the bucket and the holding pins at a certain level.

PRIOR ART LITERATURE Patent Literature

-   Patent Literature 1: Japanese Patent Publication No. 2012-101203

SUMMARY OF THE INVENTION Problem to be Solved

In the rotor, a pair of opposite convex parts (holding pins) is disposedto face each other to support the bucket in a swingable manner, andconcave parts are formed on the side surfaces of the bucket to engagewith the cylindrical surfaces of the convex parts. The concave parts ofthe bucket swing with respect to the convex parts, so as to swing thebucket to the horizontal. A reinforcing part is disposed around theconcave part of the bucket, and through improvement of the shape nearthe convex parts and the sliding surface on the side of the rotor body,in recent years, the tendency is to further increase the capacity of thebucket so as to process a large amount of sample at one time. Under thecircumstances, the amount of the sample contained in the bucketincreases, and correspondingly the size of the bucket also increases,which inevitably increases the weight. When the weight increases, thecentrifugal load applied to the holding pin will also increase, andstress concentration greater than before will occur near the base of theconvex part of the holding pin of the rotor body and increase thedeformation amount. Traditionally, improvements have been made to theshape of the holding pin or the curvature radius of the junction betweenthe holding pin and the arm to suppress deformation of the convex partof the rotor so as to reduce the stress. However, in the case of furtherincreasing the size of the bucket, the following problem occurs. Thatis, due to the increase of the centrifugal load, the conventionalreinforcing part cannot cope with the stress. It is conceivable to usealuminum alloy or stainless steel which is widely used as the materialof the rotor or the bucket, or titanium alloy which is a light andhigh-strength material. Nevertheless, because titanium alloy isexpensive and difficult to machine, the manufacturing costs will risesignificantly. Considering the design of the attachment structure of theholding pin as well as modifying the shape of the arm side that fixesthe holding pin, the inventors accomplished the invention.

In view of the above, the invention provides a centrifuge and a swingrotor for the centrifuge for reducing the stress concentrating near thebase of the convex holding pin, making it possible to increase thecapacity of the bucket that can be installed and suppress reduction inthe lifespan of the swing type rotor body.

The invention further provides a centrifuge and a swing rotor for thecentrifuge for keeping the gap between the convex (cylindrical) holdingpin and the bucket as uniform as possible during the centrifugalseparation operation and avoiding causing unnecessary vibration to thesample, so as to stabilize the centrifugal separation operation.

Solution to the Problem

According to a feature of the invention, a centrifuge includes a drivingshaft rotated by a driving means, a swing type rotor body installed onthe driving shaft, a plurality of holding pins disposed on the rotorbody, and a plurality of buckets hung on the holding pins in a swingablemanner. The rotor body includes a plurality of arm parts extendingoutward in a radial direction from a rotation center and a plurality ofbranch arms diverging at a front end of each of the arm parts on anouter peripheral side to be separated by a predetermined angle. Theholding pins are fixed to the branch arms, and a connection part isconfigured to connect two of the branch arms that diverge from the armparts on the outer peripheral side. A thickness-reduced part penetratingin the same direction as a rotation axis of the rotor body is configuredin a region surrounded by the two branch arms on an inner peripheralside of the connection part. The holding pins are protrusions formedintegrally with the rotor body and each have a cylindrical surface, andboundary portions between the branch arms and the holding pins areconnected by curved surfaces. Thus, the through thickness-reduced partis disposed while the outer peripheral side of the branch arm is held byan arc portion or a bow. Thereby, the branch arm deforms in a statesubstantially perpendicular to the holding pin, such that the stressconcentration near the convex part base of the holding pin can bealleviated.

According to another feature of the invention, a space (bucketaccommodating part) between a set of the holding pins formed on thebranch arms that extend from two adjacent arm parts of the arm parts toface the held bucket is an open structure without the connection part onthe outer peripheral side. The connection part has a cylindrical orprismatic shape, which is curved or straight, and is disposed such thata longitudinal axis of the connection part is located on an outer sidein the radial direction with respect to an intersection point of acentral axis of one of the holding pins and one of the branch armsconnected to the one of the holding pins. In this case, thethickness-reduced part has a shape similar to an outer edge shape of thebranch arms and the connection part when viewed from above, or has ashape, e.g. circle or inverted triangle, not similar to the outer edgeshape.

According to another feature of the invention, it is preferable that acircumferential thickness of the branch arm is smaller than a radialthickness of the connection part. In addition, a minimum distance r₂from the rotation center of the rotor body to the connection part isequal to or greater than a minimum distance r₁ from the rotation centerof the rotor body to the cylindrical surface of each of the holdingpins. With such a configuration, if the thickness of the arc portion orthe bow is increased and the thickness of the branch arm formed at thefront end of the arm part is reduced, excessive deformation of thebranch arm can be prevented.

Effects of the Invention

According to the invention, by forming a substantially triangular,circular, or substantially inverted triangular through thickness-reducedpart in the substantially fan-shaped or substantially triangular bucketholding part which is formed at the front end of the arm part of therotor, the branch arm is allowed to deform independently. Consequently,the deformation resulting from the centrifugal load applied on theconvex part of the holding pin can be alleviated to reduce the stressconcentrated near the base of the holding pin. Further, the lifespan ofthe swing type rotor body, which may be shortened easily due to stressconcentration, can be improved and a highly safe centrifuge can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of the centrifuge according to the invention andshows the main portions in cross-section.

FIG. 2 is a perspective cross-sectional view of the rotor assembly 2 ofthe centrifuge 1 according to an embodiment of the invention.

FIG. 3 is a bottom view of the rotor body 20 and the buckets 40 of thecentrifuge 1 according to an embodiment of the invention.

FIG. 4 is a perspective view of the bucket 40 of FIG. 1.

FIG. 5 is a transverse cross-sectional view of the rotor of thecentrifuge 1 during high-speed rotation according to an embodiment ofthe invention.

FIG. 6 is a partial plan view of the bucket holding part of the rotorbody 20 in an embodiment of the invention, in which the dotted linesindicate the deformation state in the centrifugal separation operationexaggeratedly.

FIG. 7 is an arrow view from the direction A of the rotor body 20 in anembodiment of the invention.

FIG. 8(1), FIG. 8(2), and FIG. 8(3) are partial plan views of the bucketholding part of the rotor body in the second to fourth embodiments ofthe invention.

FIG. 9 is a partial plan view of the bucket holding part of the rotorbody 120 in the conventional centrifuge, in which the dotted linesindicate the deformation state in the centrifugal separation operationexaggeratedly.

FIG. 10 is a partial plan view of the bucket holding part of the rotorbody 220 in another conventional centrifuge.

FIG. 11 is an arrow view from the direction B of the rotor body of FIG.10.

DESCRIPTION OF THE EMBODIMENTS

Embodiment 1

Hereinafter, embodiments of the invention are described with referenceto the figures. In the figures below, the same parts are assigned withthe same reference numerals, and repeated descriptions will be omitted.Moreover, in this specification, terms such as front, rear, left, right,top, bottom, inner peripheral side, and outer peripheral side refer tothe directions shown in the figures. The numerical values mentionedhereinafter also cover cases of substantially the same values. Inaddition, where a positional relationship, such as parallel, orthogonal,planar, and opposite, is mentioned, it may refer not only to completelyparallel, completely orthogonal, completely planar, and completelyopposite, but also to substantially parallel, substantially orthogonal,substantially planar, and substantially opposite.

FIG. 1 is a longitudinal cross-sectional view of a centrifuge 1 of theinvention. The centrifuge 1 includes a box-shaped case 11 and ispartitioned into an upper space and a lower space by a partition plate12 near a vertical center of the interior of the case 11. Asubstantially cylindrical bowl 4 with an open top side is accommodatedin the upper space of the partition plate 12, and a protective wall 6 isdisposed on the outer peripheral side of the bowl 4. The top side of thebowl 4 is sealed by an openable door 14, by which a rotor chamber 3 isformed. A freezing pipe 16 is wound around the bowl 4, and the interiorof the rotor chamber 3 is maintained at a desired temperature by acooling device (not shown). A rotor assembly 2 is installed in the rotorchamber 3. The rotor assembly 2 is an assembly of a swing rotor and anaccommodating cover 30 that accommodates the swing rotor. In thisembodiment, the swing rotor rotates in a state where the swing rotor isaccommodated in the accommodating cover 30. The swing rotor includes arotor body 20 installed on a driving shaft 7 a and a plurality ofbuckets 40 held swingable with respect to the rotor body 20. In theconventional swing rotor type centrifuge, the swing rotor is rotated ina state without the accommodating cover 30. In the invention, thecentrifugation operation may also be carried out without using theaccommodating cover 30. Use of the accommodating cover 30 is notnecessary to the invention.

In the lower space partitioned by the partition plate 12 in the case 11,a motor 7 serving as the driving means is accommodated in a housing 8.The housing 8 is fixed to an attaching member 13 toward the partitionplate 12 through a damper rubber 9. The motor 7 is disposed such thatthe driving shaft 7 a of the motor 7 extends in the vertical direction.The driving shaft 7 a extends from a through hole formed at the bottomof the bowl 4 to reach into the interior space of the rotor chamber 3. Acrown 7 b for transmitting a rotation torque of the driving shaft 7 a isdisposed on an upper end part of the driving shaft 7 a and the rotorassembly 2 is held by the crown 7 b. By rotating the rotor assembly 2 ata high speed, the buckets 40 are swung around the swing axis by thecentrifugal force. It is possible to remove the rotor assembly 2 fromthe rotor chamber 3 to the outside in such an assembly state. Also, in astate where the rotor assembly 2 is set in the centrifuge 1, a lid 33 ofthe accommodating cover 30 can be removed for removing the buckets 40.

An operation display section 10 is disposed on an inclined panel 15 onthe upper rear side of the case 11. The operation display section 10 isprovided to achieve functions of an input part and a display part,wherein the input part is for receiving input from the user and thedisplay part displays information to the user. The operation displaysection 10 can be made up by a plurality of buttons and a LED displaydevice, or be configured using a touch type liquid crystal display.Though not shown in FIG. 1, a controller (not shown) is provided forperforming the overall control of the centrifuge 1, such as control ofdisplay of information to the operation display section 10 and receiptof operation input from the user, control of rotation of the motor 7,control of the cooling device (not shown) for supplying a refrigerant tothe freezing pipe 16, and so on. The controller is an electronic circuitincluding a microcomputer, volatile and non-volatile storage memories,and so on.

FIG. 2 is a perspective cross-sectional view of the rotor assembly 2 ofthe centrifuge 1 according to an embodiment of the invention. The rotorassembly 2 is an assembly that accommodates the rotor body 20 (the rotorbody 20 also includes a coupling 36 attached by a screw), to which aplurality of buckets 40 are set, in the interior of the accommodatingcover 30. The accommodating cover 30 includes a shell 31, a base 32, andthe lid 33. FIG. 2 illustrates a state where the sample containers 50with the buckets 40 filled with a sample 55 are installed. The bucket 40has an inner wall shape adapted to the outer shape of the samplecontainer 50 and is manufactured by integrally molding or machining analuminum alloy. The accommodating cover 30 is used for preventing riseof the temperature, which results from the heat generated by frictionbetween air and the uneven rotor assembly 2, and reducing noise such aswind noise during rotation of the rotor assembly 2 in the centrifugalseparation operation. It is important that the accommodating cover 30has good thermal conductivity and high strength and is light in weight.Here, the accommodating cover 30 is made of a metal, such as an aluminumalloy. The base 32 having an annular shape is disposed on a loweropening part of the shell 31. The shell 31 and the base 32 form abowl-shaped container. A circular through hole is formed in the centerof the base 32. The coupling 36 is attached to the top of the throughhole for fixing the rotor body 20.

A circular opening part 31 a larger than the outer diameter of the rotorbody 20 is formed on the upper side of the shell 31. The disk-shaped lid33 is installed to the opening part 31 a of the shell 31. A knob 34 isattached to the center of the lid 33, and a through hole is formed inthe center of the knob 34. The upper front end part of a lock screw 35can be inserted into the through hole to close the opening part 31 a ofthe shell 31. Thereby, the lid 33 is only placed on top of the shell 31.The base 32 of the shell 31 and the coupling 36 can be fixed by a screwto move the accommodating cover 30 and the rotor body 20 together. Aftera fitting hole 36 a formed in the coupling 36 is set on the crown 7 b ofthe centrifuge 1 (see FIG. 1), a screw part 35 a of the lock screw 35rotatably attached to the rotor body 20 is screwed into a screw part 36b disposed on the crown 7 b, so as to fix the rotor assembly 2 to thecentrifuge 1.

Next, a detailed structure of the swing rotor (the rotor body 20 and thebuckets 40) is described with reference to FIG. 3. FIG. 3 is a bottomview of the rotor body 20 and the buckets 40 of the centrifuge 1according to an embodiment of the invention (the coupling 36 is notshown here). The rotor body 20 includes a hub 21, arm parts 23, and abucket holding part. The hub 21 is formed with a through hole 22 and hasa substantially rectangular parallelepiped outer shape. The arm parts 23are on the outer side of the hub 21 in the radial direction and extendin four directions in a cross shape when viewed from above. The bucketholding part whose outer shape is substantially fan-shaped in the topview is respectively formed at the front end portion of the aim part 23.The hub 21 is a portion disposed on the coupling 36. If the number ofthe attached buckets 40 is four, four arm parts 23 are equally spaced atan interval of a rotation angle of 90° around the rotation axis(rotation center) of the hub 21. The bucket holding part includes twobranch aims 24 and a connection arm 25. The two branch arms 24 areconnected to spread outward in a V shape in the radial direction fromthe arm part 23. The connection arm 25 serves as a connection partconnecting ends of the adjacent branch arms 24 in an arc shape. Athrough thickness-reduced part 27 is foamed between the two branch arms24 and the connection arm 25. The rotor body 20 is mainly manufacturedby precision casting of stainless cast steel or an aluminum alloy. Onlythe portions that require combining accuracy are formed integrally bycutting using machining. The through thickness-reduced part 27 is anopening portion penetrating in the axial direction of the rotation axisof the rotor. Here, the outer shape of the through thickness-reducedpart 27 in the top view is made similar to the outer shape of thesubstantially fan-shaped bucket holding part (the outer edge shape ofthe two branch arms 24 and the connection arm 25).

In terms of the positional relationship of the branch aims 24, thebranch arms 24 extend in a direction perpendicular to the rotation axis,and the branch arms 24 that face each other with the bucket 40sandwiched therebetween are parallel to each other. The concave parts ofthe bucket 40 are hung on the holding pins 26 of these parallel brancharms 24, so as to hold one bucket 40 in a swingable manner. The holdingpin 26 is formed on each of the branch arms 24 separated by the throughthickness-reduced part 27. The holding pin 26 has a substantiallycylindrical shape for supporting the bucket 40 and protrudes in a convexshape toward the side of the bucket 40. The extending direction of theholding pin 26 (the axial direction of the holding pin 26) is the sameas a tangential direction of a rotation trajectory of the rotor body 20.A concave depression (orthogonal plane 45 and so on) is formed on thebucket 40. In addition, the number of the arm parts 23, the interval(rotation angle) of the arm parts 23, and the angle between two brancharms 24 at the front end of the arm part 23 on the outer peripheral sidecan be set at will according to the number of the buckets 40 to beattached.

FIG. 4 is a perspective view of the bucket 40 used in the centrifuge 1of this embodiment. The bucket 40 is detachable from the rotor body 20.By moving the bucket 40 downward from the top (installation direction:the downward direction parallel to the axial direction), the bucket 40can be installed to the rotor body 20. The bucket 40 has an opening part41 on the top. Two protrusion parts 41 a are formed opposite to eachother on the inner side of the bucket 40. An inner space 48 foraccommodating the sample container 50 is formed downward from theopening part 41. In this embodiment, the opening part 41 of the bucket40 is in an open state. However, an openable lid may be formed on theopening part 41. The bucket 40 is manufactured by integrally molding ametal such as an aluminum alloy, for example. The bucket 40 has a cupshape that has the substantially rectangular opening part 41 when viewedfrom above. A thick part 42 where the thickness is partially increasedis formed around the opening part 41. The bucket 40 of this embodimenthas a shape that the inner space 48 is divided into two parts.

A concave part is formed on a side surface of the long side of thebucket 40. The concave part is sandwiched by the thick part 42 and twoguide ribs 43 that extend downward from the thick part 42. The concavepart is a recess when viewed from the outer side in the axial directionof the swing axis of the bucket. A width of the concave part is slightlylarger than the diameter of the holding pin 26, so as to guide theholding pin 26. A main purpose of the guide ribs 43 is to Run a guidesurface 43 a for guiding the holding pin 26. Formation of the guide ribs43 can significantly improve the rigidity of the bucket 40. In thisembodiment, a continuous groove 46 having an inverted U shape in theside view is formed in a region (bottom portion in terms of the concavepart) orthogonal to the swing axis to face the front end side of acylindrical surface of a pin receiving part 44. The orthogonal plane 45,which is a flat surface portion orthogonal to the swing axis, is formedon the inner side portion of the inverted U-shaped groove 46.

FIG. 5 is a transverse cross-sectional view of the rotor of thecentrifuge 1 during high-speed rotation according to an embodiment ofthe invention. This cross-section is taken along a plane that passesthrough the central axis (swing axis) of the holding pin 26 and thecentral axis of the bucket 40 when the bucket 40 is swung horizontallyduring high-speed rotation of the rotor body 20. The bucket 40 isswingably supported while sliding along the pin receiving part 44 of theholding pin 26. The pin receiving part 44 is in contact with thecylindrical surface 26 b of the holding pin 26, so as to support thecentrifugal load of the bucket 40. In addition, a plate-shaped bucketpartition plate 41 b is disposed from the upper side to the lower end ofthe swing axis of the bucket 40 and the rigidity of the bucket 40 isenhanced. At the moment, a strong force is applied to the holding pin 26toward the outer peripheral side. In a portion adjacent to the contactsurface of the holding pin 26 and the bucket 40, the groove 46 isformed. The groove 46 is formed on the bucket 40 and recessed towardsthe axial central side of the swing axis of the contact surface (half ofa cylindrical shape). The orthogonal plane 45 of the bucket 40 faces theholding pin 26 with a small distance therebetween in the swing axis ofthe holding pin 26 or is in contact with the holding pin 26.

Next, before describing the rotor body 20 of the centrifuge 1 of thisembodiment, the shapes of the conventional rotor bodies are describedwith reference to FIG. 9 to FIG. 11, so as to make this embodiment moreunderstandable. FIG. 9 is a plan view of (only half of) a rotor body 120of the conventional centrifuge, in which the solid lines indicate thestate when the rotation of the rotor stops and the dotted lines indicatethe deformation state in the centrifugal separation operation. Theconventional rotor body 120 includes an arm part 123 and two branch arms124, wherein the arm part 123 extends outward in a cross shape in theradial direction of a hub 121, and the two branch arms 124 extend in a Vshape respectively from the front end portion of the arm part 123. Aholding pin 126 is formed on the branch arm 124. Here, the bucketholding part includes only two straight lines (branch arms 124) and theholding pin 126. In this case, when the holding pin 126 is deformed bythe centrifugal load F of the bucket 40 and the sample, the branch arm124 deforms according to the strength of this part.

The holding pins 126 that extend coaxially are formed respectively onthe branch arm 124 indicated by the arrow b and the branch aim 124indicated by the arrow c opposite thereto. A distance D between this setof holding pins 126 is set corresponding to the size of the bucket 40 tobe installed. The space (bucket accommodating part) between the holdingpin 126 on the side of the arrow b and the holding pin 126 on the sideof the arrow c is an open structure that does not have a connection parton the outer peripheral side. In the rotor body 120 having thisconfiguration, when the rotor rotates at a high speed to swing thebucket 40, the centrifugal load F is applied on the holding pins 126toward the outer peripheral side. Consequently, the branch arms 124 aredeformed by the centrifugal load F, as indicated by the arrow 130, andthe positions of the branch arms 124 and the holding pins 126 aredeformed from the state indicated by the solid lines to the stateindicated the dotted lines (branch arms 124′ and holding pins 126).Besides, it should be noted that the deformation amount is exaggeratedin the figure to make the deformation state more understandable, anddeformation of the arm part 123 and so on outward in the radialdirection is not taken into consideration. Due to the deformation, theholding pins 126 shift to the positions of 126′. Therefore, in thecircumferential direction, the holding pins 126 deform for only adistance d₄ in the swing axis (although the distance d₄ shown in FIG. 9deviates from the swing axis, it is located on the axis). When thebranch arms 124 deform as shown by 124′ described above, the distancebetween the opposite holding pins 126 viewed in the direction of theswing axis extends from D to D+2d₄, which is unfavorable for stabilityof holding of the bucket 40. In addition, the deformation reduces thecontact area between the cylindrical surface of the holding pin 126 andthe pin receiving part 44 of the bucket 40, which increases thecentrifugal load applied on a portion of the holding pin 126 and leadsto reduction of the lifespan. To cope with this problem, it isconsidered to use a reinforcing member to connect between the brancharms 124 indicated by the arrows b and c, i.e. in the outer peripheralportion of the bucket 40, so as to fix the branch arms 124 indicated bythe arrows b and c. However, disposing such a connection member is afactor that will increase the size of the external shape of the rotorbody 120 and limit the swing range of the bucket 40. Thus, it isunfavorable. Therefore, for the rotor body 120, it is important that thestructure has no connection member in the bucket accommodating partwhere the bucket 40 swings, i.e. the open structure with no membertherein when viewed on the outer peripheral side as indicated by thearrow 131 of FIG. 9.

A rotor body 220 as shown in FIG. 10 and FIG. 11 is made as animprovement to the shape of FIG. 9. An arm part 223 and branch arms 224of the rotor body 220 are substantially the same as those of the rotorbody 120 of FIG. 9 in shape. The arm part 223 extends outward in theradial direction of a hub 221. A holding pin 226 is formed integrallywith the branch arm 224, which is also the same as the rotor body 120 ofFIG. 9. However, the rotor body 220 has a structure that the adjacentbranch arms 224 are connected by a flat plate-shaped reinforcing rib 225which extends in an arc shape. FIG. 11 is an arrow view showing therotor body 220 from the direction of the arrow B of FIG. 10. As can beunderstood from FIG. 11, the reinforcing rib 225 has a height H2 whichis sufficiently small compared to the height H near the inner peripheralend of the branch arm 224, and the reinforcing rib 225 is formed at thesame position as the attachment position of the holding pin 226 whenviewed in the vertical direction. The reason is that if the reinforcingrib 225 is thickened, the weight of the rotor body 220 increases. Bydisposing the reinforcing rib 225 as described above, it is possible toprevent the branch arms 224 from deforming and avoid deformation thatreduces an intersection angle α of the branch arms 224 (see FIG. 10).The deformation condition at the moment is indicated by the dotted linesof FIG. 10. The holding pin 226 deforms as indicated by the dotted lines226′ corresponding to the deformation of the branch arm 224 to sustainthe centrifugal load. Therefore, the portion near the base of the brancharm 224 deforms as indicated by d₆ and the front end side of the frontend surface (the surface facing the bucket 40) of the branch arm 224deforms to only d₅ at most.

The deformation amount of the rotor body 120 of FIG. 9 is large comparedto that of the rotor body 220 shown in FIG. 10, but on the other hand,the stress concentration near the base of the holding pin 126 is low.However, since there is no such reinforcing rib 225 between the pair ofopposite holding pins 126, the deformation amount d₄ increases. As aresult, the relative gap with respect to the bucket 40 increases, andthe imbalance caused by the gap worsens and may result in abnormalvibration during the rotation. On the other hand, in the rotor body 220shown in FIG. 10, the deformation amount of the branch arm 224 is smalland the deformation amount d₅ at the front end side of the holding pinis small. However, if the deformation of the branch arm 224 is hindered,a strong stress will be concentrated on the connection portion of thebranch arm 224 and the holding pin 226, especially, near an inflectionpoint of an arc surface 226 a and a planar part 224 a that are formed tosmoothly connect from the branch arm 224 to the holding pin 226 and toalleviate the stress (near the “stress concentration point” of FIG. 10).

Therefore, the invention is made. FIG. 6 is a partial plan view (solidlines) of the front end part of the rotor body 20 in an embodiment ofthe invention. In FIG. 6, the bucket holding part is formed on the frontend side (the outer side in the radial direction) of the arm part 23.The bucket holding part includes two branch arms 24, an arc-shapedconnection arm 25, and holding pins 26. The two branch arms 24 part anddiverge from the front end of the arm part 23. The connection arm 25connects the ends of the branch arms 24 on the outer peripheral side.The holding pins 26 respectively extend from the two branch arms 24. Athrough thickness-reduced part 27 is formed in the bucket holding partso as to reduce the weight and make the branch arms 24 and the holdingpins 26 deform in a controlled shape. By disposing the throughthickness-reduced part 27, the configuration is divided into the arc orbow portion of the bucket holding part (connection arm 25) and twostraight portions of a substantially fan shape (two branch arms 24). Thearm parts 23 are arranged on the rotor body 20 at an equal interval of90 degrees, and the bucket holding part being substantially fan-shapedin the top view is connected to the front end portion of the arm part23. The longitudinal axis of the connection arm 25 may be disposed topass through the outer peripheral side with respect to an intersectionof the outer peripheral surface of the branch aims 24 and the centralaxis of the holding pins 26, as indicated by the arrow 28. In addition,a minimum distance r₂ from the rotation center of the swing type rotorbody 20 of the connection arm 25 to the connection arm 25 is set equalto or greater than a minimum distance r₁ from the rotation center of theswing rotor body to the cylindrical surface of the holding pin 26. Whensuch a bucket holding part is formed and the bucket 40 is rotated at ahigh speed, the centrifugal load F of the bucket 40, the samplecontainer 50, and the sample 55 is applied on the holding pin 26, andfurther a centrifugal force is applied due to the weight of the rotorbody 20.

When the holding pin 26 is deformed by the centrifugal load F of thebucket 40 and the sample, the branch arms 24, i.e. the two straightportions of the substantially fan-shaped bucket holding part, deformaccording to the strength of this part. That is, the branch arms 24, theconnection arm 25, and the holding pins 26 of the bucket holding partdeform from the state of the solid lines to the state of the brokenlines (deformed branch arms 24′, deformed connection arm 25′, anddeformed holding pins 26′) through forces as indicated by the arrow 28 aand the arrow 28 b. Moreover, it should be noted that the deformationamount is exaggerated in FIG. 6 to make the invention moreunderstandable, and the deformation amount of the hub 21 or the arm part23 is ignored. Here, like the conventional example illustrated in FIG.10, the holding pin 26 is distorted in a way that mainly the innerperipheral side deforms only for the distance d₁, as indicated by thedotted lines, due to the centrifugal load F, and a strong stresscorresponding to the deformation is applied at the stress concentrationpoint. Since the through thickness-reduced part 27 penetrating in thesame direction as the rotation axis of the rotor body is formed in thecenter of the bucket holding part, a force as indicated by the arrow 28b is generated on the branch arm 24. Therefore, the branch arm 24 nearthe stress concentration point deforms slightly larger as indicated byd₂ and the branch arm 24 on the side of the through thickness-reducedpart 27 deforms as indicated by d₃. The configuration of this embodimentallows the deformation of d₂ and d₃, so as to prevent the stress frombeing excessively concentrated at the stress concentration point.Therefore, in the substantially fan-shaped opposite side portions(branch arms 24) of the bucket holding part, deformation of the desiredpositions (the inner peripheral side slightly inward with respect to thestress concentration point) is allowed. Here, referring to theconventional example of FIG. 10, the substantially fan-shaped oppositeside portions (branch arms 24) of the bucket holding part have verylittle deformation amount (deformation corresponding to d₂ and d₃ ofFIG. 6) because of the reinforcing rib 225. Thus, only the holding pin26 deforms and causes the stress at the stress concentration point toincrease. With the configuration of this embodiment, the centrifugalload can be sustained not only by the holding pin 26 but also by thebranch arm 24, and therefore, by properly adjusting the thickness (wallthickness) and position of the arc or bow portion (connection arm 25) inthe radial direction, the relative gap between the holding pin 26 andthe bucket 40 can be suppressed to the minimum and the swing rotor forthe centrifuge can lower the stress concentration and reduce theimbalance caused by the gap and have a long lifespan. Here, acircumferential thickness T₁ of the branch arm 24 may be smaller than aradial thickness T₂ of the connection arm 25, i.e. the connection part.

FIG. 7 is an arrow view from the direction A of the rotor body 20 in anembodiment of the invention. Specifically, the direction A is the arrowA shown in FIG. 6. As known from this figure, a height H1 of theconnection arm 25 is smaller than a height H of the arm part 23 but issubstantially equal to a height of the narrowed front end portion of thebranch arm 24. By such formation, the portion from the upper end to thelower end of the outer peripheral portion of the branch arm 24, which isformed thinner than a radial thickness T₂ of the connection arm 25 (seeFIG. 6), can be held. Thus, the overall deformation of the branch arm 24(the deformation as shown in FIG. 9) can be suppressed effectively.Further, in FIG. 7, it can be understood that the holding pin 26 is aprotrusion formed integrally with the rotor body 20 and has acylindrical surface 26 b, and boundary portions of the branch arm 24 andthe holding pin 26 are connected by a curved arc surface 26 a.

Embodiment 2

The second embodiment of the invention is described below. In the firstembodiment described above, the through thickness-reduced part 27 has ashape similar to the outer edge shape of the branch arms 24 and theconnection part 25 in the top view. In the second embodiment, however,the thickness-reduced part is formed in a shape not similar to the outeredge shape of the branch arms and the connection part. FIG. 8(1) is apartial plan view of the bucket holding part of a rotor body 60 in thesecond embodiment of the invention. The arm parts 23 are arranged on therotor body 60 at an equal interval to extend outward in the radialdirection, and a bucket holding part 64 being substantially fan-shapedis formed on the front end portion of the arm part 23. The bucketholding part 64 has a structure that is made by integrally forming theconnection portion with the branch arms, which form two straightportions in a substantially fan shape or opposite side portions in asubstantially triangular shape. Two through holes 67 that are circularin the top view are formed near the center of the bucket holding part 64to penetrate in the axial direction of the rotor. Instead of disposingthe through hole 67 at a random position, it is particularly preferableto form the center of the through hole 67 on an imaginary circle, so asto overlap the imaginary circle that passes through the stressconcentration points (the center coincides with the center of the rotorbody 60). In this way, an inner peripheral portion 67 a and an outerperipheral portion 67 b with respect to the imaginary circle that passesthrough the stress concentration points exist in the through holes 67.By such formation, the portion of the bucket holding part 64 on theouter peripheral side of the through holes 67 has the same function asthe connection arm and thus can effectively prevent the V-shaped brancharm portions from deforming close to each other (deformation thatreduces the intersection angle a when compared with FIG. 10). Further,since the portion of the branch arm near the stress concentration pointis allowed to deform slightly, the stress near the base of the holdingpin 66 (particularly, the stress concentration point) can be reduced.Because it is easy to perform the cutting work for opening the throughholes 67, the configuration of this embodiment can suppress increase ofthe manufacturing costs of the rotor body 60.

Embodiment 3

FIG. 8(2) is a partial plan view of the bucket holding part of a rotorbody 70 in the third embodiment of the invention. The arm parts 23 arearranged on the rotor body 70 at an equal interval to extend outward inthe radial direction, and a bucket holding part being substantiallytriangular is formed on the front end portion of the arm part 23. Thebucket holding part includes two branch arms 74, holding pins 76, and arod-shaped connection arm 75. The two branch arms 74 diverge in a Vshape from the front end of the arm part 23. The holding pin 76 isformed integrally with the branch arm 74. The connection arm 75 connectsthe front end sides of the two branch arms 74. The connection arm 75 maybe shaped like a round bar or a square bar. The connection arm 75 may beformed integrally with the branch arms 74 or individually. Here, theattachment position of the connection arm 75 is set such that thelongitudinal axis of the connection arm 75 is located on the outer sidein the radial direction to the extent indicated by the arrow 79 withrespect to the intersection point of the central axis of the holding pin76 and the surface of the branch arm 74 on the bucket side. By suchformation, since the through thickness-reduced part 77 is formed and theportion of the branch arm 74 near the stress concentration point isallowed to deform like the first embodiment, the stress near the base ofthe holding pin 76 (particularly, the stress concentration point) can bereduced.

Embodiment 4

FIG. 8(3) is a partial plan view of the bucket holding part of a rotorbody 80 in the fourth embodiment of the invention. Instead of formingthe large through thickness-reduced part 27 (see FIG. 6) like the firstembodiment, in the fourth embodiment, the through thickness-reduced parthas a shape that the portions near the middle in the circumferentialdirection are connected in the radial direction. Thus, a connection part85 is formed by a circumferential connection arm 85 a and a radialconnection arm 85 b. Consequently, two through thickness-reduced parts87 are formed. Here, the through thickness-reduced parts 87 may bedisposed to overlap the imaginary circle (the center coincides with thecenter of the rotor body 60) that passes through the stressconcentration points. The position or shape is set such that an innerperipheral portion 87 a and an outer peripheral portion 87 b withrespect to the imaginary circle passing through the stress concentrationpoints exist in the through thickness-reduced part 87. In the fourthembodiment, due to formation of the radial connection arm 85 b, theweight of the bucket holding part increases compared to the firstembodiment. However, the thickness T₃ of the branch arm 84 at the stressconcentration point is reduced correspondingly. By such formation, sincethe portion of the branch arm 84 near the stress concentration point isallowed to deform properly like the first embodiment, the stress nearthe base of the holding pin 86 (particularly, the stress concentrationpoint) can be reduced.

As described above, according to this embodiment, the bucket holdingpart of the rotor body is formed with the through thickness-reduced partwithout using expensive materials and the portion of the branch arm towhich the holding pin is attached is configured to deform easily. Thus,the deformation amount of the opposite side portions of the bucketholding part can be properly adjusted to reduce stress concentrationnear the base of the holding pin, reduce the imbalance caused by the gapbetween the holding pin and the bucket, and achieve the centrifuge andthe swing rotor for the centrifuge with long lifespan. Although theinvention has been described above based on the embodiments, theinvention should not be construed as limited to the aforementionedembodiments, and various modifications may be made without departingfrom the spirit of the invention.

What is claimed is:
 1. A swing rotor for a centrifuge, comprising: aplurality of holding pins disposed on a swing type rotor body; and aplurality of buckets hung on the holding pins in a swingable manner,wherein the rotor body comprises a plurality of arm parts extendingoutward in a radial direction from a rotation center and a plurality ofbranch arms diverging at a front end of each of the arm parts on anouter peripheral side to be separated by a predetermined angle, and theholding pins are fixed to the branch arms, wherein a connection part isconfigured to connect two of the branch arms diverging from the armparts on the outer peripheral side, and a thickness-reduced partpenetrating in a same direction as a rotation axis of the rotor body isconfigured in a region surrounded by the two branch arms on an innerperipheral side of the connection part, wherein a circumferentialthickness of one of the branch arms connected to the connection part issmaller than a radial thickness of the connection part, and the holdingpins are protrusions formed integrally with the rotor body and eachcomprise a cylindrical surface, and boundary portions between the brancharms and the holding pins are connected by curved surfaces includingconvex base parts, such that during a centrifugal separation operationthe branch arms deform in a state substantially perpendicular to theholding pins, such that stress concentrations near the convex base partsof the holding pins are alleviated.
 2. The swing rotor for thecentrifuge according to claim 1, wherein a space between a set of theholding pins formed on the branch arms that extend from two adjacent aimparts of the a parts to face the held bucket is an open structurewithout the connection part on the outer peripheral side.
 3. The swingrotor for the centrifuge according to claim 2, wherein the connectionpart has a columnar shape and is disposed such that a longitudinal axisof the connection part is located on an outer side in the radialdirection with respect to an intersection point of a central axis of oneof the holding pins and one of the branch arms connected to the one ofthe holding pins.
 4. The swing rotor for the centrifuge according toclaim 3, wherein the thickness-reduced part has a shape similar to anouter edge shape of the branch arms and the connection part when viewedfrom above.
 5. A centrifuge, comprising a driving shaft rotated by adriving device and a swing type rotor body installed on the drivingshaft, wherein: the rotor body is the rotor body according to claim 4.6. The swing rotor for the centrifuge according to claim 3, wherein thethickness-reduced part has a shape not similar to the outer edge shapeof the branch arms and the connection part when viewed from above.
 7. Acentrifuge, comprising a driving shaft rotated by a driving device and aswing type rotor body installed on the driving shaft, wherein: the rotorbody is the rotor body according to claim
 3. 8. A centrifuge, comprisinga driving shaft rotated by a driving device and a swing type rotor bodyinstalled on the driving shaft, wherein: the rotor body is the rotorbody according to claim
 2. 9. The swing rotor for the centrifugeaccording to claim 1, wherein a minimum distance from the rotationcenter of the rotor body to the connection part is equal to or greaterthan a minimum distance from the rotation center of the rotor body tothe cylindrical surface of each of the holding pins.
 10. A centrifuge,comprising a driving shaft rotated by a driving device and a swing typerotor body installed on the driving shaft, wherein: the rotor body isthe rotor body according to claim 1.